A prior art interactive television system is shown generally in FIG. 1. The system includes a digital video data provider 1, decoders 3a-c for converting the digital video data to an analogue format, a television 5 at each decoder for displaying the video data, and enhanced content transmitted over a network 2. In current systems, the enhanced content is transmitted to decoders, or set-top boxes (STBs), which then display pages of enhanced content on a television. A user input device 4 is provided at each decoder 3a-c so that a user can adjust settings of the decoder and/or the television 5 and respond to queries or questions in the enhanced content. The user input device 4 could, for example, be a keypad or remote control.
The enhanced content is typically content available to be displayed at the direct or indirect request of a user onto a television screen. The enhanced content is typically in addition to the basic A/V (audio/visual) data of a television program or movie. It may consist of information, such as news, television schedules, or weather reports, or may invite a response from a user.
Enhanced content may be transmitted over a network independently of A/V data, or alternatively may be embedded in the A/V data.
The term “interactive television” suggests that a viewer can provide input to the system, for example to respond to queries within the enhanced content or to control the video stream that he receives. An example of a user input/response is an answer to a question posed in the enhanced content (or interactive content). If the video content being displayed on a television is, for example, a quiz show, it may be desirable to provide interactive content consisting of quiz questions corresponding to those being asked in the quiz show.
FIG. 2 shows in more detail the decoding arrangement of a prior art interactive television system. A network 2 provides decoder 3 with a stream of enhanced content 8, together with an indication of the required flow of that content. The flow will normally be indicated by reference to a video stream that that enhanced content accompanies. The enhanced content 8 is inputted to a formatting unit 9 for formatting its input signal into a series of pages 10a-d of enhanced content for display on television 5.
Each page 10a-d could have associated with it a time at which it is to be displayed on the television. In this implementation, referring to the example shown in FIG. 2, the pages 10a-d are associated with a television program which commences at 16.30. The first page, 10a, is to be displayed at 16.31. The second page, 10b is to be displayed at 16.32, and 10c and 10d are to be displayed at 16.38 and 16.40 respectively.
This arrangement has a number of disadvantages. Firstly, the broadcast schedule must be known by the provider of enhanced content in advance of the transmission of the stream of enhanced content 8. In this way, the time at which each page of enhanced content is to be displayed can be embedded into the stream 8 before transmission. In addition to the enhanced content provider requiring information regarding the start time of each television program for which it is providing enhanced content, it also needs information on the timing of any scheduled intermissions in each program.
Secondly, this arrangement for the display of enhanced content is incapable of making adjustments to accommodate changes to the advertised broadcast schedule. Similarly, the arrangement cannot accommodate unadvertised intermissions in the broadcast. These could occur if the broadcast has to be interrupted for some reason. Also, if the broadcast is to be interrupted by advertisements the position and duration of the advertising breaks must be taken into account when the enhanced content is set up. If the broadcast is to be shown on a number of channels which have different advertising schedules then the enhanced content must be set up for each one. As a result, enhanced content for one program may continue to be displayed after that program has been interrupted.
In order to mitigate these problems it is known to provide a series of indications together with the video content. These allow a component of the broadcasting network to broadcast enhanced content associated with a particular video stream on receipt of indications identifying the video stream.
The indications are preferably sent at regular intervals, and identify a video stream (representing a particular show) and a time position within the show. The network component responsible for broadcasting enhanced content can determine precisely when the enhanced content should be sent, and it can also broadcast trigger signals to individual decoders to which the decoders respond by playing out the enhanced content to a viewer of the show.
However, if a periodic indication related to a video stream is not received at the broadcasting component of the network, the enhanced content and the triggers will not be sent and the enhanced content will therefore not be played out to viewers. While this is desirable when, for example, a TV show has ended or during a scheduled break (such as an advertisement break), in some situations it could be a disadvantage since play-out might also be interrupted at times when this is not desired if an indication is not received at the network component due to low signal strength.
It is desirable that there should be an improved way in which the display of enhanced content is synchronised with a video or other signal to which it is related.